//
//  Shaders.metal
//  MetalRenderer
//
//  Created by Stuart Carnie on 5/31/18.
//  Copyright © 2018 Stuart Carnie. All rights reserved.
//

// File for Metal kernel and shader functions

#include <metal_stdlib>
#include <simd/simd.h>

// Including header shared between this Metal shader code and Swift/C code executing Metal API commands
#import "ShaderTypes.h"

using namespace metal;

#pragma mark - functions using projected coordinates

vertex ColorInOut basic_vertex_proj_tex(const Vertex in [[ stage_in ]],
                                        const device Uniforms &uniforms [[ buffer(BufferIndexUniforms) ]])
{
    ColorInOut out;
    out.position = uniforms.projectionMatrix * float4(in.position, 1.0);
    out.texCoord = in.texCoord;
    return out;
}

fragment float4 basic_fragment_proj_tex(ColorInOut in [[stage_in]],
                                        constant Uniforms & uniforms [[ buffer(BufferIndexUniforms) ]],
                                        texture2d<half> tex          [[ texture(TextureIndexColor) ]],
                                        sampler samp                 [[ sampler(SamplerIndexDraw) ]])
{
    half4 colorSample = tex.sample(samp, in.texCoord.xy);
    return float4(colorSample);
}

#pragma mark - functions for rendering sprites

vertex FontFragmentIn sprite_vertex(const SpriteVertex in [[ stage_in ]], const device Uniforms &uniforms [[ buffer(BufferIndexUniforms) ]])
{
    FontFragmentIn out;
    out.position = uniforms.projectionMatrix * float4(in.position, 0, 1);
    out.texCoord = in.texCoord;
    out.color    = in.color;
    return out;
}

fragment float4 sprite_fragment_a8(FontFragmentIn  in  [[ stage_in ]],
                              texture2d<half> tex [[ texture(TextureIndexColor) ]],
                              sampler samp        [[ sampler(SamplerIndexDraw) ]])
{
    half4 colorSample = tex.sample(samp, in.texCoord.xy);
    return float4(in.color.rgb, in.color.a * colorSample.r);
}

#pragma mark - functions for rendering sprites

vertex FontFragmentIn stock_vertex(const SpriteVertex in [[ stage_in ]], const device Uniforms &uniforms [[ buffer(BufferIndexUniforms) ]])
{
    FontFragmentIn out;
    out.position = uniforms.projectionMatrix * float4(in.position, 0, 1);
    out.texCoord = in.texCoord;
    out.color    = in.color;
    return out;
}

fragment float4 stock_fragment(FontFragmentIn  in  [[ stage_in ]],
                              texture2d<float> tex [[ texture(TextureIndexColor) ]],
                              sampler samp         [[ sampler(SamplerIndexDraw) ]])
{
    float4 colorSample = tex.sample(samp, in.texCoord.xy);
    return colorSample * in.color;
}

#pragma mark - filter kernels

kernel void convert_bgra4444_to_bgra8888(device uint16_t *              in  [[ buffer(0) ]],
                                         texture2d<half, access::write> out [[ texture(0) ]],
                                         uint                           id  [[ thread_position_in_grid ]])
{
    uint16_t pix = in[id];
    uchar4 pix2 = uchar4(
                         extract_bits(pix,  4, 4),
                         extract_bits(pix,  8, 4),
                         extract_bits(pix, 12, 4),
                         extract_bits(pix,  0, 4)
                         );

    uint ypos = id / out.get_width();
    uint xpos = id % out.get_width();

    out.write(half4(pix2) / 15.0, uint2(xpos, ypos));
}

kernel void convert_rgb565_to_bgra8888(device uint16_t *                in  [[ buffer(0) ]],
                                         texture2d<half, access::write> out [[ texture(0) ]],
                                         uint                           id  [[ thread_position_in_grid ]])
{
    uint16_t pix = in[id];
    uchar4 pix2 = uchar4(
                         extract_bits(pix, 11, 5),
                         extract_bits(pix,  5, 6),
                         extract_bits(pix,  0, 5),
                         0xf
                         );

    uint ypos = id / out.get_width();
    uint xpos = id % out.get_width();

    out.write(half4(pix2) / half4(0x1f, 0x3f, 0x1f, 0xf), uint2(xpos, ypos));
}